Several polymers have been described in the art as being degradable, biodegradable, compostable, and the like. However, the polymers typically suffer from some limitation in physical properties which detracts from their utility in a number of applications. For example, for economic reasons it is typically desirable to process polymers by a melt process such as melt spinning, cast film extrusion, or blown film extrusion. However, the melt strength and/or set time of the polymer may not be suitable for good melt processing. Thus, the product tends to tear, break, or stick during processing, or the product may be unacceptably nonuniform in its physical properties. Once processed, still other properties may be needed to meet the converting, storage (including shipping and warehouse storage), or end use requirements of the polymeric product. More particularly, the product may need certain mechanical and thermomechanical properties to withstand subsequent processing and storage, and to meet end use requirements.
In addition, although several polymeric materials have been described as biodegradable, not all biodegradable materials are readily compostable. In general, for a material to be compostable, the polymeric product or large fragments thereof must undergo an initial breakup to much smaller fragments during the initial stages of a typical, commercial composting process. Otherwise, the products or large fragments may be screened out of the compost stream and may never become part of the final compost.
In commercial composting processes, the product is typically exposed to mechanical action, elevated temperatures, and/or moisture to promote the initial breakup of the product or large fragments thereof to much smaller fragments. Many biodegradable polymers exist which are sensitive to mechanical action, elevated temperatures, or moisture, such that they would individually meet the initial requirements for composting. However, few, if any, also possess the mechanical, thermomechanical, and other properties required for their practical use in a number of applications.
One practical application of biodegradable polymeric materials is in disposable absorbent articles. Although disposable absorbent articles largely comprise materials which would be expected ultimately to degrade, and although articles of this type contribute only a very small percentage of the total solid waste materials generated by consumers each year, nevertheless, there is currently a perceived need to devise such disposable products from materials which are more readily biodegraded and, preferably, which are more readily composted. There is a particular perceived need to replace polyethylene backsheets in absorbent articles with liquid impervious films of biodegradable material, since the backsheet is typically one of the largest non-biodegradable components of a conventional disposable absorbent article.
In addition to being biodegradable, the films employed as backsheets for absorbent articles must satisfy many other performance requirements. For example, the polymer must be thermoplastic if economical, conventional, film melt processing methods, such as cast film and blown film extrusion and extrusion coating, are to be employed. Preferred materials can be melt processed into films that have substantially uniform physical properties and physical integrity. In addition, the film should have sufficient thermomechanical integrity. Thus, upon exposure to elevated temperatures, the film should maintain sufficient physical integrity to enable it to function as required at the elevated temperature, for example, to enable it to survive converting processes. In addition, even after exposure to elevated temperatures, the film should have substantial physical integrity. The film should also have certain properties to meet end use requirements. More particularly, properties such as tensile strength, tensile modulus, tear strength, impact strength, and moisture transmission rate are important since they influence the absorbent article's durability and containment while being worn.
It is an object of the present invention to provide a polymeric composition that is biodegradable and which can be melt processed to form products having substantially uniform physical properties and physical integrity. Another object is to provide such a polymeric composition that also has thermomechanical integrity. Thus, upon exposure to elevated temperatures, a product thereof should maintain sufficient physical integrity to enable it to function as required at the elevated temperature, for example, to enable it to survive converting processes. In addition, even after exposure to elevated temperatures, the product should have mechanical and other properties which enable it to be suitable for use in a number of practical applications. It is a further object of the invention to provide such a polymeric composition that can be used to form more readily compostable products. Another object of the present invention is to provide such products in the form of a fiber, nonwoven, or film. Yet another object of the present invention is to provide disposable absorbent articles such as disposable diapers, catamenials, and the like, having component parts formed from such products.
It is a particular object of the present invention to provide biodegradable, liquid impervious films suitable for use in absorbent articles, wherein the film has each of the following properties at room temperature:
a) a machine direction (MD) tensile modulus of from about 10,000 to about 100,000 lbs/in.sup.2 (6.895.times.10.sup.8 dynes/cm.sup.2 to 6.895.times.10.sup.9 dynes/cm.sup.2 ; 68.95 MPa to 689.5 MPa); PA1 b) a machine direction tear strength of at least about 25 grams per 25.4 microns (25.4 micrometers, 1 mil) of thickness; PA1 c) a cross machine direction (CD) tear strength of at least about 25 grams per 25.4 microns (25.4 micrometers, 1 mil) of thickness; PA1 d) an impact strength of at least 12 cm as measured by falling ball drop; PA1 e) a moisture transport rate of less than about 0.0012 grams per square centimeter per 16 hours; and PA1 f) a thickness of from about 12 microns (12 micrometers, 0.5 mils) to about 75 microns (75 micrometers, 3 mils). PA1 where n has a range of 3 to 4.5 and x has a range of 150 to 3000. Commercially, HPC is available from Hercules Inc. under the tradename KLUCEL.
Preferred films also have, at room temperature and in the machine direction of manufacture, an elongation at break of at least about 140% and a tensile strength of at least 20 MPa. In addition, preferred films have a failure temperature, as defined herein, of at least about 60.degree. C.